[SRU][B][F][PATCH 0/1] kernel: s390/cpum_cf, perf: change DFLT_CCERROR counter name (LP: 1891454)

[frank.heimes at canonical.com]

Buglink: https://bugs.launchpad.net/bugs/1891454

SRU Justification:

[Impact]

* Change the counter name DLFT_CCERROR to DLFT_CCFINISH on IBM z15 to avoid confusion.

* This counter counts completed DEFLATE instructions with exit code 0, 1 or 2.

* And since exit code 0 means success and exit code 1 or 2 indicate errors the name can be ambiguous.

[Fix]

* Rename s390 z15 counter named DFLT_CCERROR to DFLT_CCFINISH.

* Backport Focal: https://launchpadlibrarian.net/493272507/0001-s390-cpum_cf-perf-change-DFLT_CCERROR-counter-name.patch

* Backport Bionic: https://launchpadlibrarian.net/493439681/u18-0001-s390-cpum_cf-Add-new-extended-counters-for-IBM-z15.patch

[Test Case]

* Enable hardware counters in the activation profile of a z15 LPAR.

* Just check the countername in sysfs with: ls /sys/devices/cpum_cf/events/{DFLT_CCERROR,DFLT_CCFINISH}

[Regression Potential] 

* The regression potential can be considered as low, since:

* Counters like these are usually not activated by default and need to be explicitly enabled.

* No code functionality is changed with that patch, only a renaming is done at 3 places in one code file arch/s390/kernel/perf_cpum_cf_events.c as well as in /tools/perf/pmu-events/arch/s390/cf_z15/extended.json.

* The fix got already upstream accepted in 5.8-rc7, hence it got upstream reviewed,

* and the modifications are limited to s390x, are only relevant for the z15 / LinuxONE III hw generation that are relatively new.

* Issue with the renaming I can think of are that people don't know about the new name and may look for the old one and don't find it anymore,

* and with that also if the old counter name is used in scripts or applications, these may fails due to an unknown counter name.

[Other Info]

* The backports are based on commit 3d3af181d370069861a3be94608464e2ff3682e2 ("s390/cpum_cf,perf: change DFLT_CCERROR counter name") that is upstream accepted since v5.8-rc7.

* Hence this SRU is not requested for groovy, since it's already in groovys kernel 5.8 in proposed, but only requested for focal and bionic.

Thomas Richter (1):
  s390/cpum_cf,perf: change DFLT_CCERROR counter name

 arch/s390/kernel/perf_cpum_cf_events.c               | 4 ++--
 tools/perf/pmu-events/arch/s390/cf_z15/extended.json | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

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2.25.1